1. Field of the Invention
The present invention relates to a nonaqueous electrolyte battery and, more specifically, to improvement of nonaqueous electrolytes in order to obtain a nonaqueous electrolyte battery having excellent storage stability.
2. Description of the Prior Art
In recent years, much attention has been paid to batteries utilizing lithium as a negative electrode active material, since they have a high energy density and can provide high voltages.
Since lithium is extremely reactive with water, batteries of this type use nonaqueous electrolytes. For such electrolytes, there are used solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, tetrahydrofuran, 1,3-dioxolane and mixtures of the foregoing; and solutes such as LiPF.sub.6, LiCF.sub.3 SO.sub.3, LiClO.sub.4, LiBF.sub.4, LiN(CF.sub.3 SO.sub.2).sub.2 and LiAsF.sub.6.
Conventional nonaqueous electrolyte batteries, however, have the problem of their capacity decreasing during storage thereof, caused by decomposition of the nonaqueous electrolyte by reaction with the negative electrode. In particular, with use of a carbon material such as graphite or coke as the negative electrode material, the battery capacity decreases to a large extent after the battery has been charged and stored. Accordingly, the above problem of self-discharge has been a particularly serious problem with nonaqueous electrolyte batteries using a carbon material as the negative electrode material.
As a result of an intensive study to solve the problem, the present inventors have found that addition of a specified amount of a specific material to the nonaqueous electrolyte suppresses the reaction (self-discharge) of the electrolyte with the negative electrode, thereby improving the storage stability.